1999 Mercedes Benz 300td A/C FANS ON CONSTANTLY

HI,

I AM HAVING A PROBLEM WITH THE TWO A/C FANS IN MY CAR. AS SOON AS YOU TURN ON THE IGNITION THE FANS START RUNNING. THIS PROBLEM STARTED WHEN I RESET THE SERVICE SENSORE AFTER COMPLETING THE OIL CHANGE. NOW I DONT KNOW HOW TO SET IT BACK.